Steve Grant, former London district secretary of Aslef, the train drivers' union, described Crow as a "tough negotiator and a good colleague to have behind you".

"There will never, ever be another Bob Crow," he added.

Unison general secretary, Dave Prentis, said: "I am shocked and saddened to hear of the death of Bob Crow. Unison members will want to send their sympathy to his family and friends.

"Bob was a tough, no-nonsense union leader who always did his best for his members, and it was very much down to his tough stance that their pay and conditions improved.

"Despite all the flak he got, he stood his ground and was a great member of our trade union family. His loss will be felt across the whole trade union movement."

Communication Workers Union general secretary Billy Hayes said: "Bob Crow was a great leader and he was a great inspiration to rail workers and trade unionists around the world.

"Bob will be greatly missed. He will be remembered for his passion, his commitment and his endless pursuit for social justice. His death is a tragedy and I would like to send my deepest condolences to his family and friends."